Another wall sounds good to me!! I did a big clean up one evening also which involved putting bleach out, and I don't see them resting themselves as much since!! Yippee!!
Apart from anything else, as far as I can see, teenagers like these are opportunistic, have a short attention span and are lazy. They'll probably just move on.
Absolutely nobody. You could rig one up in the ComReg offices and I doubt they'd realise.
Unless you had one powerful enough to knock your whole neighbourhood offline but even then I imagine you'd have a panicked emergency callout from the ESB before the mobile phone companies.